Abstract

Space photovoltaics is dominated by multi‐junction (III‐V) technology. However, emerging applications
will require solar arrays with high specific power (kW/kg), flexibility in stowage and
deployment, and a significantly lower cost than the current III‐V technology offers. This research
demonstrates direct deposition of thin film CdTe onto the radiation‐hard cover glass that is normally
laminated to any solar cell deployed in space. Four CdTe samples, with 9 defined contact
device areas of 0.25 cm2, were irradiated with protons of 0.5‐MeV energy and varying fluences.
At the lowest fluence, 1 × 1012 cm−2, the relative efficiency of the solar cells was 95%. Increasing
the proton fluence to 1 × 1013 cm−2 and then 1 × 1014 cm−2 decreased the solar cell efficiency to
82% and 4%, respectively. At the fluence of 1 × 1013 cm−2, carrier concentration was reduced by
an order of magnitude. Solar Cell Capacitance Simulator (SCAPS) modelling obtained a good fit
from a reduction in shallow acceptor concentration with no change in the deep trap defect concentration.
The more highly irradiated devices resulted in a buried junction characteristic of the
external quantum efficiency, indicating further deterioration of the acceptor doping. This is
explained by compensation from interstitial H+ formed by the proton absorption. An anneal of
the 1 × 1014 cm−2 fluence devices gave an efficiency increase from 4% to 73% of the pre‐irradiated
levels, indicating that the compensation was reversible. CdTe with its rapid recovery through
annealing demonstrates a radiation hardness to protons that is far superior to conventional multijunction
III‐V solar cells.